Caption: UFO in a black hole, computer artwork. This could represent the belief that alien craft are able to use black holes as portals to travel across space and time. A black hole is a region in space where the pull of gravity exceeds the velocity of light. It is only visible from the effects it has on its surroundings, and its intense gravity distorts the light passing nearby. A black hole is formed when a sufficiently-massive star has used up the fuel that sustained its nuclear fires. The resulting loss of outwards heat pressure allows a catastrophic total collapse of the star under its own weight.